Pivoting or oscillating torsional hinged mirrors provide very effective yet inexpensive replacements for spinning polygon shaped mirrors in printers and some types of displays. As will be appreciated by those skilled in the art, torsional hinged mirrors may be MEMS type mirrors etched from a silicon substrate using processes similar to those used in the manufacture of semiconductor devices. Many torsional hinged mirrors provide a raster type scan for printers and displays and operate at rotational speeds of about 3 KHz. However, as the demand for higher print speeds and better resolution increases, flatness of the mirror reflective surface has now become a much more serious problem. As the mirror continuously flexes or bends back and forth during the continuous oscillations about the axis, the greatest deformation is at the tip or ends of the flexing mirror. Presently available mirrors have substantially reduced this problem by the use of several bonded layers of material such as silicon. Unfortunately, manufacturing a mirror comprised of two or more layers significantly increases costs. In addition, the greater rotational speeds and demand for thinner mirrors, has also resulted in some flexing of the mirror around the edges of the mirror during operation.
More specifically, referring to the prior art FIG. 5A, there is illustrated a single piece torsional hinged device 10 such as a mirror or other optical surface that oscillates on its torsional hinges 12a and 12b about a pivoting axis 14. Although perhaps exaggerated, the cross-sectional view of FIG. 5B illustrates how the top half of an optical surface portion or mirror 16 of device 10 flexes during a complete pivoting cycle. This type of excessive flexing is unacceptable, although some flexing can be tolerated for many applications. As discussed above, the excessive flexing may be solved by a multi-layer mirror or device. However, for many uses, the multi-layer mirrors or devices are too expensive.
Therefore, it would be advantageous to provide an inexpensive torsional hinged optical surface or mirror that has reduced flexing. Other optical surfaces, such as refractive surfaces, would also benefit from the teachings of this invention.